The meniscus is the fibrous cartilage in the knee joint. It protects the bone’s surfaces from impact, diffuses forces and provides stability. When children tear the meniscus, it often can be repaired. But when it is torn badly, it is often resected (cut out), leaving the child without this key structure. The lateral (outside) part of the knee is the most sensitive to any meniscus cartilage loss in children — but loss of any significant portion of the meniscus cartilage leads to pain, swelling and early arthritis. The incidence of such tears is about 61 per 100,000 people each year. Yet the repair/replacement ratio is well under 10 percent for repair and 0.01 percent for replacement. Why?
Meniscus regeneration and replacement in children is a growing field, though unfortunately still small. In children who still have open growth plates (i.e., their bones are still growing), surgeons sometimes tell parents to wait until growth is finished before risking surgery. Their concern is that the growth plate might be injured, leading to growth arrest and deformity. This fear, however, must be balanced against the following facts.
First, there is nearly a 100 percent chance of early arthritis if a child loses the entire meniscus and probably greater than a 90 percent chance if they lose the posterior horn of the tissue. The earlier the tissue is repaired, regenerated or replaced, the less damage occurs. Modern techniques of meniscus transplantation do not require permanent stitches to be used — and the growth plates can be protected by creating very small drill holes above the plate. So waiting for further growth is unwise.
Another concern is whether or not a donor meniscus will grow with the child or how long it will last. There are no long-term studies of meniscus replacement in children published in the medical literature, but what we have seen in our meniscus replacement practice over the last 25 years has been promising.
The story is similar for meniscus regeneration. A collagen meniscus implant (CMI) that can induce regrowth of the meniscus tissue upon a trellis-like structure is now available. The CMI has been used in more than 5,000 adult cases and has demonstrated successful tissue regrowth in multiple clinical trials. Logically, children should be able to re-grow their tissue even better than adults — yet unfortunately, there are no reported cases of the CMI being used in children.
Lastly, the surgical techniques and instruments for meniscus repair, regeneration and replacement have improved dramatically. The reasons for not utilizing these techniques to protect injured knees should override excuses from the past, especially given the consequences of tissue removal alone.
Sometimes, in medicine and surgery, all that parents and doctors have to go on is common sense, experience, and probabilities of success. We know that meniscus injuries are devastating to the knee. We know how to regenerate and replace them even if we cannot yet guarantee they will last or protect the joint the way the original meniscus did. But without large multicenter study with long-term data, many insurance plans won’t agree to reimburse the procedure. Common sense says they should. Children’s knees say they must.
Dr. Kevin R. Stone is an orthopedic surgeon at The Stone Clinic and chairman of the Stone Research Foundation in San Francisco.